It is often desirable to estimate the position (or “location”) of persons and things in a geographic area with a reasonable degree of accuracy. Accurate estimations of a position can be used to speed up emergency response times, track business assets, and link a consumer to a nearby business. Various techniques are used to estimate the position of an object. One such technique relies on transmission of signals from geographically-distributed transmitters to a mobile device that are used to estimate “ranges” (i.e., distances) between each transmitter and the mobile device. These ranges may then be used during a process called trilateration to estimate the position of the mobile device.
Systems such as a Global Navigation Satellite System (GNSS) combine “ranging” and “data” signals into one signal, and then transmit that combined signal to a GNSS receiver of a mobile device. The ranging signal is used to calculate the range between the mobile device and the satellite. The data signal provides information about the transmitter. One type of GNSS referred to as the Global Positioning System (GPS) modulates assistance data onto a ranging signal (e.g., at a rate of 50 bits per second). There are problems with this modulation approach. One problem is a low data rate. Another problem is a less accurate estimate of the range between the mobile device and a transmitter, mainly because the modulation approach does not allow for long coherent integration of the ranging signal from that transmitter. Another problem is that the cross-correlation between the data and ranging signals causes difficulties in resolving multipath in the ranging signals. Yet another problem is that the data signal need not be transmitted every time the ranging signal is transmitted, and doing so unnecessarily consumes network resources.
Accordingly, there is a need for improved techniques of transmitting ranging signals and data signals while maintaining desired accuracy of position estimates.